The disclosure of Japanese Patent Application No. 2000-231174 filed on Jul. 31, 2000, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a valve timing control apparatus and a valve timing control method for an internal combustion engine.
2. Description of Related Art
Internal combustion engines, such as vehicle-installed engines and the like, are provided with valve timing control apparatus for varying the engine valve timing for the purpose of output increase, emission improvement, etc. An example of such valve timing control apparatus is described in Japanese Patent Application Laid-Open No. 11-210424.
The valve timing control apparatus described in the aforementioned laid-open patent application includes a variable valve timing mechanism that varies the relative rotation phase of a camshaft with respect to the crankshaft of the internal combustion engine based on the fluid pressure in a timing advance-side pressure chamber and the fluid pressure in a timing retard-side pressure chamber. An oil control valve operates to adjust the oil pressure in the two hydraulic chambers based on a predetermined control quantity, and a lock mechanism and a stopper mechanism fix the relative rotation phase of the camshaft in a predetermined advanced state in which the relative rotation phase is advanced by a predetermined amount from a most retarded state. During idle operation, the valve timing control apparatus performs a control so as to bring the relative rotation phase of the intake camshaft to a nearly most retarded state, so that suitable intake valve timing will be achieved. Furthermore, using the lock mechanism and the stopper mechanism, the valve timing control apparatus sets a control range of valve timing control such that the valve timing reaches a startup timing. The valve timing control apparatus fixes the relative rotation phase via the lock mechanism and the stopper mechanism at engine start-up, and discontinues the fixation of the relative rotation phase during an ordinary engine operation, thereby preventing the reduction of the control range of valve timing control while optimizing the valve timing at engine start-up.
During the course of stopping the internal combustion engine during which the engine revolution speed gradually decreases from an idle revolution speed, the aforementioned valve timing control apparatus changes the relative rotation phase of the intake camshaft from a phase near the most retarded state that is suitable for the idle operation, to the vicinity of a phase corresponding to the start-up timing, that is, to a predetermined range that is slightly to the advanced side of the phase corresponding to the start-up timing. After changing the relative rotation phase, the valve timing control apparatus is able to fix the relative rotation phase to a phase that is suitable for a start-up operation, by using the lock mechanism and the stopper mechanism. During the course of engine stopping, the valve timing control apparatus changes the relative rotation phase of the intake camshaft to the advanced side, that is, to the phase corresponding to the start-up timing, by setting the control quantity of the oil control valve to a value that maximizes the oil pressure in the timing advance-side hydraulic chamber.
With this setting of the control quantity during the engine course of stopping, the relative rotation phase is first changed to a phase (predetermined advanced state) on the advanced side of the phase corresponding to the start-up timing. Then, as the oil pressure in the timing advance-side hydraulic chamber decreases with decreases in the engine revolution speed, the relative rotation phase changes toward the phase corresponding to the start-up timing in a direction to the retarded side because the reaction force involved in the opening and closing of the intake valves acts on the intake camshaft as a rotating torque toward the retarded side. Thus, during the engine stopping process, the valve timing control apparatus changes the relative rotation phase to the phase corresponding to the start-up timing, so as to establish a state in which the aforementioned fixation by the lock mechanism and the stopper mechanism can be performed.
Furthermore, this valve timing control apparatus changes the relative rotation phase immediately before the stopping of the engine is initiated (during the idle operation), to an appropriate state beforehand in accordance with a parameter, such as the idle revolution speed or the like, that affects the oil pressure in the timing advance-side hydraulic chamber during the idle operation, so that at the time of completion of the stopping of the engine, the relative rotation phase reaches the vicinity of the phase corresponding to the start-up timing. By changing the relative rotation phase for the idle operation beforehand in the above-described manner, it becomes possible to precisely bring the relative rotation phase to the vicinity of the phase corresponding to the start-up timing, when the stopping of the engine is completed.
However, if the relative rotation phase is changed during the idle operation as described above, the idle operation of the engine may become unstable since the changed relative rotation phase is not an optimal phase for the idle operation.
It is one object of the invention to provide an internal combustion engine valve timing control apparatus capable of changing the relative rotation phase of a camshaft to a vicinity of a predetermined advanced state (a phase corresponding to the start-up timing) during the course of stopping the engine, without altering the relative rotation phase during the idle operation from an appropriate state.
In accordance with one aspect of the invention, an internal combustion engine valve timing control apparatus includes: a variable valve timing mechanism, a stopper, a fluid pressure adjustor and a control quantity controller. The variable valve timing mechanism varies a relative rotation phase of a camshaft with respect to a crankshaft of an internal combustion engine based on a fluid pressure in a timing advance-side hydraulic chamber and a fluid pressure in a timing retard-side hydraulic chamber. The stopper (fixing means) fixes the relative rotation phase of the camshaft at a predetermined advanced state that is advanced from a most retarded state by a predetermined amount, with respect to at least a timing retarded side. The fluid pressure adjustor (fluid pressure adjusting means) is controlled based on a predetermined control quantity to adjust the fluid pressure in the timing advance-side hydraulic chamber and the fluid pressure in the timing retard-side hydraulic chamber. The control quantity controller (control quantity setting means) sets the control quantity so that the relative rotation phase of the camshaft becomes a state that is on an advanced side of the predetermined advanced state during a course of stopping the internal combustion engine, and then sets the control quantity to a value that holds the relative rotation phase of the camshaft.
According to the above-described construction, the control quantity used to control the fluid pressure adjustor is set (fixed) to a value that holds the relative rotation phase of the camshaft after the relative rotation phase has changed to the advanced side of the predetermined advanced state during the course of stopping the internal combustion engine. During this state, the relative rotation phase of the camshaft is held near the predetermined advanced state and on the advanced side thereof. Therefore, during the course of stopping the engine, the relative rotation phase of the camshaft changes to the vicinity of the predetermined advanced state independently of the state of phase occurring during the idle operation preceding the initiation of stopping the engine. Hence, the control apparatus is able to set the relative rotation phase of the camshaft to a phase suitable for the idle operation during the idle operation preceding the stopping of the engine, and to change the relative rotation phase of the camshaft precisely to the vicinity of the predetermined advanced state during the course of stopping the engine.